Hypertension is a continuous, independent, yet modifiable risk factor for cardiovascular, cerebrovascular and renal disease. It has been estimated that 62% of cerebrovascular disease and 49% of ischemic heart disease can be attributed to sub-optimal blood pressure control. For this reason one of the most commonly performed test in a doctor's surgery is blood pressure measurement.
The measurement of brachial blood pressure using an inflatable cuff, results in a systolic blood pressure reading and a diastolic blood pressure reading. The readings are typically in millimeters of mercury mmHg (a mmHg being equivalent to 133.3223684211 pascals (Pa)). A number of factors can affect the accuracy of these blood pressure readings, and the following table lists some of these (Handler, Joel, The Permanente Journal/Summer 2009/Volume 13 No. 3, pages 51-54).
Factors affecting accuracy of blood pressure measurementsMagnitude of systolic/diastolicblood pressure discrepancyFactor(mmHG)Talking or active listening10/10Distended bladder15/10Cuff over clothing5-50/Cuff too small 10/2-8Smoking within 30 minutes of6-20/measurementParalyzed arm2-5/Back unsupported6-10/Arm unsupported, sitting 1-7/5-11Arm unsupported, standing6-8/
Even when the above factors are taken into account, another factor, which can affect the accuracy of the reading is the “white coat effect” (WCE). Thus, the blood pressure in certain individuals will rise when a doctor takes the blood pressure reading, particularly in the doctor's surgery.
Automated blood pressure devices are known, which are designed to negate any WCE errors for an individual. Thus, the bpm-100, manufactured by BPTru Ltd, of Unit 1, 1850 Hartlet Avenue, Coquitlam, BC, Canada V3K 7A1, is an automated blood pressure monitor, which, without an operator's assistance, takes six blood pressure readings, discards the first one and automatically computes the average of the remaining five readings.
However, a problem with this approach is that, even though a doctor/operator is not involved, the individual's blood pressure readings may still be elevated, as he has not reached a relaxed state before the taking of the readings commences.
In most cases, this inaccuracy is caused by two contributing factors: a failure to allow the cardiovascular and nervous systems to reach a completely stable parasympathetic state and an inability to identify when this state has been reached.
When the body is at rest the human heart rate drops causing a corresponding drop in blood pressure (BP) across the peripheral vascular system. In order to maintain adequate delivery of blood to peripheral tissues the system must compensate for the drop in BP by increasing blood flow. It does this by dilating the vessels. As the heart rate lowers, the sympathetic nervous system controlling vasoconstriction is turned off and the parasympathetic nervous system is activated, causing vasodilation. It can, in some cases, take time for the cardiovascular system to reach this completely stable parasympathetic state due to environmental or physiological conditions. Failure to wait for this completely stable parasympathetic state to be reached will result in an inaccurate BP reading and could lead to the misdiagnosis of a patient's blood pressure status; this applies both to hypertension and hypotension.
Thus, there is a need for a device for measuring brachial blood pressure in an individual which provides accurate blood pressure readings and avoids the aforementioned situations leading to inaccurate readings.
Furthermore, there is a need for a device, which will give accurate results outside the clinical setting, when used, for example as a home blood pressure monitor.